Hammer bit locking mechanism

ABSTRACT

A hammer bit retainer system includes a hammer bit locking mechanism arranged and designed to prevent decoupling of a driver sub from a hammer casing. The hammer bit locking mechanism includes an expandable split ring which is disposed in the coupling between the driver sub and hammer casing. The hammer bit locking mechanism prevents axial movement of the driver sub relative to the hammer casing in at least one direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of related U.S. ProvisionalApplication Ser. No. 61/654,498 filed Jun. 1, 2012, titled “Hammer BitLocking Mechanism,” to Bhatia et al. and U.S. Provisional ApplicationSer. No. 61/747,691 filed Dec. 31, 2012, titled “Hammer Bit LockingMechanism,” to Bhatia et al., the disclosures of which are incorporatedby reference herein in their entirety.

BACKGROUND

Percussion bit assemblies are often used in drilling or boring throughthe Earth's surface. In a percussion bit assembly, a percussion hammeris used to drive a percussion bit into the ground. The percussion hammeruses the reciprocating action of a piston to energize the bit.

FIG. 1 illustrates a conventional percussion bit assembly 100. Thepercussion bit assembly 100 includes a hammer case 122 that connects toa lower end of a drill string (not shown) through a threaded pinconnection 102. The lower end of the hammer case 122 is threadablyengaged 144 with a driver sub 140. A plurality of splines (not shown)disposed on the driver sub 140 engage a plurality of splines 116disposed on a shank 114 of a hammer bit 110, and rotate to drive the bit110. A retainer 160, e.g., a conventional split ring, is disposed aroundan upper end of the shank 114 of the hammer bit 110 and abuts the driversub 140. The retainer 160 retains the hammer bit 110 in the percussionbit assembly 100. The retainer 160 may be held in place, initially, byan elastic ring 106, or o-ring, to facilitate assembly of the bit 110and driver sub 140 with the hammer case 122. The retainer 160 isconfined by the inner wall of the hammer case 122 to maintainring-to-bit engagement. The upper end of the hammer bit 110 includes apiston strike surface 108 and a foot valve 104, or blow tube. The lowerend of the hammer bit 110 includes a head 112.

During certain operations performed with the percussion bit assembly100, the drill pipe may reverse its rotation, thereby causing the driversub 140 to back off, or unthread, from the hammer case 122.Occasionally, the driver sub 140 will unintentionally back off downholedue to torsional oscillations, known as “stick-slip” of the drillstring. If the driver sub 140 backs off, the bit 110 and the driver sub140 remain at the bottom of the borehole.

The drill string components, which may include a drill pipe, abottomhole assembly, a driver sub, etc., may be coupled by variousthread forms known as connections, or tool joints, any of which mayunthread or back off. When a drill string becomes stuck downhole, thedriver sub may unintentionally back off downhole, or the drill stringmay be backed off from the driver sub to recover as much of the drillstring as possible. The back off may be intentionally accomplished byapplying reverse torque and detonating an explosive charge inside aselected threaded connection. The back off may be also be accomplishedby applying tension to the drill string and detonating an explosivecharge, thereby allowing the threads to slide by each other withoutturning.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

A hammer bit locking mechanism is disclosed. The hammer bit lockingmechanism includes a driver sub, a hammer casing and a locking devicedisposed therebetween. The driver sub is adapted to receive and movablycouple to the shank of a bit, e.g., percussion bit. The driver sub alsoincludes a portion having an outer surface with one or more groovestherein. The hammer casing has a central bore and receives at least aportion of the driver sub in its central bore. A locking device, e.g.,an expandable split ring, is disposed between the hammer casing and aportion of the driver sub. The locking device includes an inner surfacewith one or more grooves therein configured to engage the one or moregrooves in the outer surface of the portion of the driver sub. Thelocking device is further arranged and designed to prevent axialmovement of the driver sub relative to the hammer casing in at least onedirection.

A method of preventing the decoupling of coupled components of apercussion hammer bit is also disclosed. The method includes inserting alocking device, e.g., an expandable split ring, in a circumferentialcavity positioned in a hammer casing and expanding the locking device.The method also includes inserting at least a portion of a driver subinto a central bore of the hammer casing and through the expandedlocking device. The method further includes coupling the driver sub andthe hammer casing such that one or more inner surface grooves of thelocking device engage one or more outer surface grooves of the driversub, thereby preventing axial movement between the driver sub and thehammer casing in at least one direction.

A locking mechanism of a downhole tool is also disclosed. The downholetool includes a first body adapted to receive and movably couple to theshank of a bit, e.g., a percussion bit. The downhole tool also includesa second body having a central bore, which receives a portion of thefirst body in the central bore. A first split ring is disposed betweenthe second body and a portion of the first body. The first split ringincludes an inner surface with one or more grooves formed therein and anouter surface with one or more grooves formed thereon. The first splitring is arranged and designed to prevent axial movement of the firstbody relative to the second body in at least one direction. A secondsplit ring is disposed radially within the first split ring. The secondsplit ring includes an outer surface with one or more grooves formedthereon, which are configured to engage the one or more grooves in theinner surface of the first split ring.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a cross-sectional view of a conventional hammer bitassembly.

FIG. 2 depicts a perspective view of an illustrative hammer bit lockingmechanism in a hammer bit assembly, according to one or more embodimentsdisclosed

FIG. 3 depicts a cross-sectional view of the hammer bit lockingmechanism of the hammer bit assembly of FIG. 2.

FIG. 4 depicts a perspective view of an illustrative hammer case of thehammer bit assembly, according to one or more embodiments disclosed.

FIG. 5 depicts a perspective view of an illustrative driver sub,according to one or more embodiments disclosed.

FIG. 6 depicts a perspective view of an illustrative expandable splitring, according to one or more embodiments disclosed.

FIG. 7 depicts the installation of an illustrative hammer bit lockingmechanism in a hammer bit assembly, according to one or more embodimentsdisclosed.

FIG. 8 depicts the installation of the hammer bit locking mechanism ofFIG. 7 during steady state operation.

FIG. 9 depicts the engagement of the hammer bit locking mechanism ofFIG. 7 to prevent disassembly of the hammer bit assembly.

FIG. 10 depicts the removal of the hammer bit locking mechanism of FIG.7 when disassembly of the hammer bit assembly is desired.

FIG. 11 depicts a perspective view of an illustrative lug disposed inconjunction with a hammer bit locking mechanism in a hammer assembly,according to one or more embodiments disclosed.

FIG. 12 depicts a perspective view of the lug of FIG. 11.

FIG. 13 depicts a perspective view of an illustrative hammer bit lockingmechanism, according to one or more embodiments disclosed.

FIG. 14 depicts a perspective view of the hammer casing of FIG. 13.

FIG. 15 depicts a perspective view of the expandable split ring of FIG.13.

FIG. 16 depicts a cross-section view of an illustrative hammer bitlocking mechanism, according to one or more embodiments disclosed.

FIG. 17 depicts a perspective view of the expandable split ring of FIG.16.

FIG. 18 depicts a perspective view of a driver sub of FIG. 16.

FIG. 19 depicts a cross-sectional view of an illustrative hammer bitassembly having first and second split rings, where inner surfacegrooves of the first split ring cover about 100% of an axial length ofthe first split ring and outer surface grooves of the second split ringcover about 100% of an axial length of the second split ring, accordingto one or more embodiments disclosed.

FIG. 20 depicts a cross-sectional view of the illustrative hammer bitassembly, where the inner surface grooves of the first split ring coverabout 75% of the axial length of the first split ring and the outersurface grooves of the second split ring cover about 75% of the axiallength of the second split ring, according to one or more embodimentsdisclosed.

FIG. 21 depicts a cross-sectional view of the illustrative hammer bitassembly, where the inner surface grooves of the first split ring coverabout 50% of the axial length of the first split ring and the outersurface grooves of the second split ring cover about 50% of the axiallength of the second split ring, according to one or more embodimentsdisclosed.

FIG. 22 depicts a cross-sectional view of the illustrative hammer bitassembly, where the inner surface grooves of the first split ring coverabout 25% of the axial length of the first split ring and the outersurface grooves of the second split ring cover about 25% of the axiallength of the second split ring, according to one or more embodimentsdisclosed.

FIG. 23 depicts a cross-sectional view of the illustrative hammercasing, where the second split ring has been omitted and the outersurface grooves in the first split ring have been omitted, according toone or more embodiments disclosed.

FIG. 24 depicts a cross-sectional view of the illustrative hammercasing, where the outer surface grooves in the first split ring havebeen omitted, according to one or more embodiments disclosed.

DETAILED DESCRIPTION

The following is directed to various illustrative embodiments of thedisclosure. The embodiments disclosed should not be interpreted, orotherwise used, as limiting the scope of the disclosure, including theclaims. In addition, those having ordinary skill in the art willappreciate that the following description has broad application, and thediscussion of any embodiment is meant only to be illustrative of thatembodiment, and not intended to suggest that the scope of thedisclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claimsrefer to particular features or components. As those having ordinaryskill in the art will appreciate, different persons may refer to thesame feature or component by different names. This document does notintend to distinguish between components or features that differ in namebut not function. The figures are not necessarily to scale. Certainfeatures and components herein may be shown exaggerated in scale or insomewhat schematic form and some details of conventional elements maynot be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion and, thus, should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first component is coupled to a secondcomponent, that connection may be through a direct connection, orthrough an indirect connection via other components, devices, andconnections. Further, the terms “axial” and “axially” generally meanalong or parallel to a central or longitudinal axis, while the terms“radial” and “radially” generally mean perpendicular to a centrallongitudinal axis.

Additionally, directional terms, such as “above,” “below,” “upper,”“lower,” etc., are used for convenience in referring to the accompanyingdrawings. In general, “above,” “upper,” “upward,” and similar termsrefer to a direction toward the Earth's surface from below the surfacealong a borehole, and “below,” “lower,” “downward,” and similar termsrefer to a direction away from the surface along the borehole, i.e.,into the borehole, but is meant for illustrative purposes, and the termsare not meant to limit the disclosure.

Referring generally to FIG. 2, a hammer bit locking mechanism 220 isdisclosed. The hammer bit locking mechanism 220 may include a driver sub240 adapted to receive and movably couple to the shank 114 of a bit 110(not shown but see, e.g., FIG. 1). The driver sub 240 may include aportion having an outer surface with one or more grooves 246 therein. Ahammer casing 222 may have a central bore 230 and receive the portion ofthe driver sub 240 in the central bore 230 (FIG. 3). An expandable splitring 260 may be disposed between the hammer casing 222 and the portionof the driver sub 240. The expandable split ring 260 may include aninner surface with one or more grooves 264 (FIG. 6) therein configuredto engage the one or more grooves 246 in the outer surface of theportion of the driver sub 240. The expandable split ring 260 may bearranged and designed to prevent axial movement of the driver sub 240relative to the hammer casing 222 in at least one direction.

One or more embodiments disclosed herein relate to a hammer bit lockingmechanism 220 in a hammer assembly 200. Such hammer bit lockingmechanism 220 acts to prevent vibration-initiated back offs (i.e.,loosening and separation) of the hammer bit threaded connection. As usedherein, the term “back off” refers to the unscrewing of drill stringcomponents downhole. Referring generally to FIGS. 2-6, an illustrativehammer bit locking mechanism 220 and components thereof in accordancewith one or more embodiments of the present disclosure are shown. Asshown in FIGS. 2 and 3, and as will be disclosed in greater detailhereinafter, a first body 240 is threadably coupled to an end portion(e.g., lower end portion) 236 of a second body 222. The first body 240may be a generally cylindrical driver sub, and the second body 222 maybe a hammer casing 222, and the first and second bodies 240, 222 arereferred to as such in the following description.

As best shown in FIGS. 3 and 4, the hammer assembly 200 has a generallycylindrical casing 222 with a central bore 230 therethrough and internalthreads 228 on an inner surface thereof. In FIG. 3, a circumferentialcavity 238 is defined within the central bore 230 between the innersurface of the hammer casing 222 and the outer wall of the driver sub240. The inner surface of the hammer casing 222, defining thecircumferential cavity 238, may have one or more female grooves 226formed therein. The female grooves 226 may be configured having grooveprofiles such as square, trapezoidal, triangular, round or elliptical,and other profiles known to those skilled in the art. The grooveprofiles may be configured having chamfers on the root or crestinterfaces or both. In one or more embodiments, the groove profiles maybe symmetrical, while in other embodiments, the groove profiles may beasymmetrical. Further still, the groove profiles may be configured in ahooked configuration.

Returning to FIG. 2, the hammer casing 222 of the hammer assembly 200further includes an access window 224 disposed in an outer wall thereoffor access to the central bore 230, e.g., when the driver sub 240 is notpresent, and the circumferential cavity 238, e.g., when the driver sub240 is present. The access window 224 is positioned to be substantiallycentered within an axial length of the circumferential cavity 238 formedwhen driver sub 240 is coupled to the lower end portion 236 of thehammer casing 222. The access window 224 may be any number of variousshapes and configurations, for example, square, circular, etc. Further,to prevent ingress of foreign particles into the hammer casing 222, theaccess window 224 may be sealed with a resin or other sealing component,which may be removed from the access window 224 to provide access to thecircumferential cavity 238.

As briefly disclosed above and best shown in FIGS. 2-3, the hammerassembly 200 includes a generally cylindrical driver sub 240 havingexternal threads 248 on an outer surface 258 of an upper end portion 252thereof (see, e.g., upper end portion 252 of driver sub 240 shown inFIG. 5). As shown in FIGS. 3 and 4, the external threads 248 areconfigured to engage internal threads 228 on an inner surface of thehammer casing 222. The driver sub 240 is configured to be stabbed (i.e.,inserted) into the hammer casing 222, and the external threads 248 areconfigured to be threadably engaged with the corresponding internalthreads 228 of the hammer casing 222. As best shown in FIG. 5, thedriver sub 240 further includes a series of external circumferentialgrooves 246 on an outer surface 258 thereof. In one or more embodiments,the external circumferential grooves 246 are located proximate theexternal threads 248 in a substantially central region 254 of the driversub 240 along an axial length thereof. The circumferential externalgrooves 246 of the driver sub 240 may be configured having symmetricalor asymmetrical groove profiles. Thus, in one embodiment, the driver subexternal grooves 246 may have a “saw tooth” groove profile. In anotherembodiment, the external grooves 246 may be configured having a “hooked”configuration.

In one or more embodiments, the driver sub 240 may be tapered along anaxial length thereof from its upper end portion 252 towards its lowerend portion 256. In other words, the upper end portion 252 of the driversub 240 may have an initial diameter that gradually increases axiallytoward the lower end portion 256. Thus, the driver sub 240 may have asomewhat conical axial profile. In tapered driver sub embodiments, suchtaper may have an angle of between 0 degrees and 30 degrees, between 0degrees and 10 degrees, or between 0 degrees and 5 degrees. The taper ofthe driver sub 240 may be used to expand a locking device 260 (notshown), during assembly, as will be described in further detail below.For example, and returning to FIG. 3, the tapered profile of the driversub 240 may expand a locking device 260 positioned circumferentiallyabout the driver sub 240 during assembly of the hammer casing 222 andthe driver sub 240. In another embodiment, the driver sub 240 may betapered along its axial or longitudinal length on one axial orlongitudinal side (i.e., in one hemisphere), while the other side (i.e.,opposite hemisphere) is substantially perpendicular between upper andlower end faces thereof.

The hammer bit locking mechanism 220 further includes a locking device260 (shown in FIG. 6) disposed in the circumferential cavity 238 of thehammer casing 222. In one or more embodiments, the locking device 260 isan expandable split ring, as further disclosed below. Within thecircumferential cavity 238, the locking device 260 is arranged anddesigned to engage an outer surface 258 of the driver sub 240 atexternal circumferential grooves 246 and an inner surface of the hammercasing 222 at female grooves 226. As will be discussed in greater detailhereinafter, this engagement of the locking device 260 with externalcircumferential grooves 246 and female grooves 226 acts to prevent thethreaded connection (i.e., corresponding external threads 248 andinternal threads 228) between the hammer casing 222 and the driver sub240 from backing off (i.e., rotating and separating).

As illustrated in FIG. 6, an expandable split ring embodiment of lockingdevice 260 includes grooves 262 on an outer surface thereof (i.e., outersurface grooves 262) and grooves 264 on an inner surface thereof (i.e.,inner surface grooves 264). The outer surface grooves 262 of the splitring 260 are configured to engage corresponding internal grooves 226 ofthe hammer casing 222. In one or more embodiments, the outer surfacegrooves 262 of the split ring 260 may have coarser grooves with a largerpitch (i.e., fewer grooves per axial distance) than the inner surfacegrooves 264 of the split ring 260. In another embodiment, the innersurface grooves 264 of the split ring 260 may have coarser grooveshaving a larger pitch than the outer surface grooves 262 of the splitring 260. In still further embodiments, the outer surface grooves 262and the inner surface grooves 264 of the split ring 260 may have groovesof substantially equal pitch. The outer surface grooves 262 of the splitring 260 may be configured having groove profiles which are square,trapezoidal, triangular, round or elliptical, and of other profilesknown to those skilled in the art. Further, these groove profiles may besymmetrical or asymmetrical. In one or more embodiments, the outersurface grooves 262 are arranged and designed with chamfers at either orboth root and crest interfaces.

The inner surface grooves 264 of the split ring 260 are arranged anddesigned to engage corresponding external grooves 246 on the outersurface 258 of the driver sub 240. In one or more embodiments, the innersurface grooves 264 are fine-pitched with respect to the outer surfacegroove 262 and, thus, configured to engage similarly fine-pitchedexternal grooves 246. The inner surface grooves 264 may have asymmetrical or asymmetrical groove profile. In one such asymmetricalembodiment, the inner surface grooves 264 may have a “hooked” grooveconfiguration. In another such asymmetrical embodiment, the innersurface grooves 108 have a “saw tooth” groove profile but with a taperedsurface that peaks at a substantially radially vertical surface, andwhich corresponds with a groove profile of circumferential grooves 246.Engagement of the asymmetrical groove profile of the inner surfacegrooves 264 of the split ring 260 with corresponding outer surfacegrooves 246 of the driver sub 240 permits axial movement of the driversub 240 in one direction (i.e., threading), thus preventing axialmovement of the driver sub 240 in the opposite direction (i.e.,unthreading), as will be disclosed in greater detail hereinafter.

Turning now to FIG. 7, the assembly of the locking device 260 within thecircumferential cavity 238 between the lower end portion 236 of thehammer casing 222 and the upper end portion 252 of driver sub 240 isillustrated in a cross-sectional view. When the driver sub 240 isinstalled/stabbed into the hammer casing 222, the driver sub 240 willmove relative to the hammer casing 222 in the direction of arrow 266.The driver sub 240 engages the split ring 260, such that the split ring260 is expanded over the outside surface of driver sub 240. As disclosedpreviously, the driver sub 240 may be tapered to facilitate thisexpansion. The external circumferential grooves 246 permit relativemotion between driver sub 240 and the split ring 260 to occur in onedirection. The orientation of ramp 276 on the external circumferentialgrooves 246 with the corresponding ramp 286 on the inner surface grooves264 of the split ring 260 permits the diameter of the split ring 260 toenlarge as the ramps 276, 286 slide past each other. The contactinterface of the ramps 276, 286, being in a non-perpendicularorientation relative to axial movement (as indicated by arrow 266),permits the relative motion between the split ring 260 and the driversub 240 to in turn provide sufficient radial force on the split ring 260to expand the diameter of the split ring 260, thereby facilitating thedriver sub 240 movement in the direction of arrow 266 relative to thesplit ring 260.

On the opposite side of the split ring 260, the outer surface grooves262 of the split ring 260 engage the female grooves 226 of the hammercasing 222. The outer surface grooves 262 and female grooves 226 have acorresponding set of flats, i.e., 288, 298 on the outer surface grooves262 and female grooves 226, respectively, which are perpendicular to themovement of the driver sub 240, as shown by arrow 266. The outer surfacegrooves 262 also have ramps, e.g., 294 on the female grooves 226, whichcorrespond to the ramps, e.g., 284 on the outer surface grooves 262.When the driver sub 240 is moving in the direction of arrow 266, theflats 288, 298 on the outer surface grooves 262 and female grooves 226,respectively, are engaged such that the axial movement of the split ring260 relative to the driver sub 240 in the direction of arrow 266 isarrested. However, when the driver sub 240 is moving in the direction ofarrow 266, the flats 288, 298 are engaged such that perpendicularmovement relative to arrow 266 is permitted, and the ramps 246, 264 mayclimb past each other during assembly/stabbing of the driver sub 240 inthe hammer casing 222.

The hammer bit locking mechanism 220 is assembled such that the driversub 240 is inserted/stabbed into the hammer casing 222 with the lockingdevice 260 disposed in the circumferential cavity 238 between an innersurface of the hammer casing 222 and an outer surface of the driver sub240, as best shown in FIG. 8. In this steady state illustration, theramp 286 and the flat 282 of the split ring 260 constrict around andsettle into mating contact with the ramp 276 and the flat 272 of thedriver sub 240. In this steady state position, the ramp 294 and the flat298 on the female grooves 226 of the hammer casing 222 may not be inengaging contact with corresponding/mating ramp 284 and flat 288 on theouter surface grooves of the locking device 260. In one or moreembodiments, a slight amount of clearance may exist between theseaforementioned corresponding surfaces. The steady state position, asillustrated in FIG. 8, is the service position when the assembly 200 isin operational use and the anti-back feature of the locking mechanism220 is not engaged.

When the assembly 200 is in operation, severe vibration and/or improperoperational practices may create an undesirable condition in which thedriver sub 240 begins to move in the direction of arrow 268, asillustrated in FIG. 9. This motion, in the direction of arrow 268, iscreated when the driver sub 240 begins to rotate and unthread itselffrom the hammer casing 222 at corresponding engaged threads 228, 248(see, e.g., FIG. 3). If left unabated, the driver sub 240 will freeitself from the hammer casing 222 and become separated from the hammercasing 222. However, when the locking mechanism 220 of one or moreembodiments of the present disclosure is employed, the unabated movementof the driver sub 240 in the direction of arrow 268 is prevented, asfurther disclosed hereinafter.

Continuing with FIG. 9, if the driver sub 240 begins to loosen from thehammer casing 222, the driver sub 240 moves axially in the direction ofarrow 268 relative to the hammer casing 222. However, in this movementdirection 268, the split ring 260 is mechanically locked by the contactof the flats 272 of the external circumferential grooves 246 of thedriver sub 240 and the flats 282 of the inner surface grooves 264 of thesplit ring 260, such that both the driver sub 240 and the split ring 260move together as a single unit. Such unified axial movement willcontinue freely until arresting contact is made between the ramps 294 onthe female grooves 226 of the hammer casing 222 and the ramps 284 on theouter surface grooves 262 of the split ring 260. If additional force isapplied to the driver sub 240 in the direction of arrow 268, the ramps294, 284 engage further forcing the split ring 260 to apply a hoopstress around the driver sub 240, such that the mating contacting forceof the flats 272, 282 is increased. Due to the hoop stress created bythe ramps 294, 284 acting on the flats 272, 282, a mechanical lock isgenerated between the driver sub 240, the split ring 260 and the hammercasing 222, thereby halting any further axial movement of the driver sub240 in the direction of arrow 268 relative to the hammer casing 222.

The split ring 260 may be expandable (i.e., a diameter of the split ring260 may be enlarged from an initial collapsed diameter) and may beconfigured having two end portions with a gap therebetween to allow thesplit ring 260 to radially expand. The split ring 260 may be configuredto radially expand to up to about 10%, up to about 20% or up to about30% of its original unexpanded diameter in one or more embodiments. Thesplit ring 260 may be a circular band configured having a rectangularcross-section with substantially concentric inner and outer surfaces(i.e., concentric diameters). In one or more other embodiments, thesplit ring 260 may be configured having non-concentric inner and outersurfaces (i.e., non-concentric diameters). For example, across-sectional thickness of the split ring 260 may be tapered along awidth of the split ring 260 cross-section. In one or more otherembodiments, the locking device 260 may be a two-piece split ring whichis installed separately to form a single locking device 260 in thecircumferential cavity 238. In still other embodiments, the split ring260 may have a wedge-shaped cross-section.

As illustrated in FIG. 10, to remove the driver sub 240 from the hammercasing 222 when the split ring 260 is in place (e.g., to service theassembly 200) the split ring 260 is expanded such that the ramps 276,286 as well as the flats 272, 282 are separated with a sufficientclearance to permit the driver sub 240 to move in the direction of arrow268 without contacting the split ring 260. Such separation isaccomplished using a spreading tool inserted into access window 224 (notshown in FIG. 9; see, e.g., FIG. 2) and in between the split 270 of thesplit ring 260 (FIG. 6). A separation force is applied to spread the twoend portions of the split ring 260, thereby increasing the diameter ofthe split ring 260. At a maximum separation of the end portions of thesplit ring 260, the ramps 294, 284 as well as the flats 288, 298 will bein mating contact. This expanded diameter of the split ring 260 providesthe maximum clearance between the split ring 260 and the driver sub 240and provides more than adequate clearance between the split ring 260 andthe driver sub 240 to unthread driver sub 240 from the split ring 260 atcorresponding engaged threads 228, 248 (see, e.g., FIG. 3).

In certain embodiments, the split ring 260 may be manufactured fromalloy steel. For example, steel may be alloyed with a variety ofelements in total amounts of between 1.0% and 50% by weight to improveits mechanical properties (e.g., strength, toughness, hardness, wearresistance, hardenability). In certain embodiments, the split ring 260may be heat treated. Common alloys that may be used include, but are notlimited to, manganese, nickel, chromium, molybdenum, vanadium, siliconand boron. Other alloys that may be used include, but are not limitedto, aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tinand zirconium. In other embodiments, the split ring 260 may bemanufactured from a non-alloy steel. In still other embodiments, thesplit ring 260 may be manufactured from other metallic materials. Infurther embodiments, the split ring 260 may be manufactured fromnon-metallic materials.

Now turning to FIGS. 11 and 12, a lug 290 or other device may bedisposed along with the split ring 260 to prevent the split ring 260from rotating after disposing the split ring 260 within thecircumferential cavity 238 (i.e., the end portions of the split ring 260remain in position at the access window 224 in the hammer casing 222).As illustrated in FIG. 11, the lug 290 may be disposed in the accesswindow 224 of the hammer casing 222. The lug 290 may be press fit intothe access window 224 from inside the hammer casing 222 before thedriver sub 240 is inserted into the hammer casing 222. The split ring260 is disposed in the circumferential cavity 238 such that the endportions of the split ring 260 may abut a middle section 292 of the lug290. In one or more embodiments, the lug 290 is arranged and designed tofill the void of the split 270 of the split ring 260 such that themiddle section 292 and the extended flats 291 of the lug 290 aredisposed between the end portions of the split ring 260. With the middlesection 292 of the lug 290 captured in the access window 224, the splitring 260 is thus prevented from rotating in either direction whileinstalled in the circumferential cavity 238 of the hammer casing 222.The middle section 292 of the lug 290 may also have an aperture 293through which an expander device (described in more detail hereinafter)may be inserted for expanding the split ring 260. In one or moreembodiments, the aperture 293 may be internally threaded.

The lug 290 may be an alloy steel material in one or more embodiments.In another embodiment, the lug 290 may be made from other materials or acomposite of materials. As disclosed above, the lug 290 may haveextended flats 291 on both sides of its middle section 292. In one ormore other embodiments (not shown), the lug 290 may not have anyextended flats 291, or in still one or more other embodiments (notshown), the lug 290 may have one extended flat 291 on one side of itsmiddle section 292. In such embodiments, the middle section 292 may bearranged and designed to more fully fill the void left by space 270 ofsplit ring 260. In other embodiments, the lug 290 may have externalcoarse grooves (not shown) configured to mate with female grooves 226 ofthe hammer casing 222.

Referring back to FIGS. 7-9, and as previously disclosed, the lockingmechanism 220 may be configured to allow relative axial and rotationalmovement between the hammer casing 222 and the driver sub 240 in onedirection (i.e., the driver sub 240 may be allowed to move axiallyinward into the hammer casing 222), while preventing axial movement inan opposite direction (i.e., the driver sub 240 is prevent from movingaxially outward away from the hammer casing 222). Stated otherwise, thesplit ring 260, inserted into the circumferential cavity 238, allows thedriver sub 240 to be stabbed and threaded into the hammer casing 222,but keeps the driver sub 240 from backing out of the hammer casing 222in the event the threaded connection (i.e., hammer casing threads 228and driver sub threads 248) becomes loose during operation due to theratchet engagement between the inner surface grooves 264 of the splitring 260 (FIG. 6) and outer surface threads 246 of the driver sub 240.

FIGS. 13-15 depict an illustrative locking mechanism 320, according toone or more embodiments. The driver sub 340 is stabbed and threaded intoa hammer casing 322 (threaded connection not shown), and a split ring360 is installed therebetween to prevent the driver sub 340 from backingoff. As shown in FIG. 15, the split ring 360 includes extensions 361which may be accessed through a slot 325 (FIG. 13) of the hammer casing322 when the split ring 360 is disposed between the driver sub 340 andthe hammer casing 322. The extensions 361 may include one or more smallholes/apertures 363 or other features to allow a hand tool or expanderdevice (e.g., pliers) to engage the extensions 361 and expand (orcontract) the split ring 360. In one or more embodiments, the extensions361 may be integrally formed with the split ring 360. In anotherembodiment, the extensions 361 may be separately formed and coupled tothe split ring 360, for example, by welds, adhesives, brazing or otherknown methods. Still further, the extensions 361 may be configured inany number of shapes, including square (as shown), circular or otherpolygonal shapes. The extensions 361 may be rounded (by grinding ormachining) to provide any type of shape or configuration to fit withinthe hammer casing 322 without interfering with other components butwhile also being easily accessible for expanding. The holes/apertures363 through the extensions 361 may be sized and/or shaped to accommodateany type of tool configuration that may be used to expand (or contract)the split ring 360.

FIGS. 16-18 depict an illustrative locking mechanism 420, according toone or more embodiments. The split ring 460 shown in FIG. 17 has outersurface grooves 462; however, the split ring 460 has no grooves on theinner surface. Rather, the split ring 460 has a smooth inner surface465. Outer surface grooves 462 of the split ring 460 may engage femalegrooves 426 in the circumferential cavity 438 of the hammer casing 422,while the smooth inner surface 465 of the split ring 460 is configuredto engage a smooth mating groove 445 (shown in FIG. 16) machined on theouter diameter of the driver sub 440. The mating groove 445 may beconfigured to correspond with an inner surface of the split ring 460.

As will be described below in FIGS. 19-24, a multi-piece split ring mayinclude two cooperating split rings that are engaged by ramps andgrooves. A ratio of a length of the ramps and grooves of a first splitring to a length of the ramps and grooves of a second split ring may bepre-set to provide a predetermined break-out torque. For example, in oneor more embodiments, a shear force used to shear grooves formed betweenthe first split ring and the second split ring may be predetermined by aratio between a length of outer surface grooves formed on the firstsplit ring that are engaged with the hammer casing and the length of thegrooves formed between the first split ring and the second split ring.As such, the hammer casing may be torqued in excess of the predeterminedbreak-out torque threshold relative to the driver sub such that thegrooves formed between the first split ring and the second split ringare sheared, and the hammer casing may be disengaged from the driversub. Those having ordinary skill in the art will appreciate thatembodiments show in FIGS. 19-24 can be combined with earlier embodimentsdiscussed herein, such as the embodiments shown in FIGS. 1-18.

FIGS. 19-22 show cross-sectional views of one or more embodiments of anillustrative hammer assembly 200 having a hammer bit retainer systemdisposed within a circumferential cavity between a lower end portion 236of the hammer casing 222 and an upper end portion of the driver sub 240,similar to the circumferential cavity 238 shown in FIGS. 3 and 4. In oneor more embodiments, the hammer bit retainer system may be a multi-piecering and may include a first split ring 260 and a second split ring 250radially within the first split ring 260. The first split ring 260 maybe configured to engage with the second split ring 250 within thecircumferential cavity between the hammer casing 222 and the driver sub240, e.g., the circumferential cavity 238 shown in FIGS. 3 and 4. In oneor more embodiments, the circumferential cavity between the hammercasing 222 and the driver sub 240 may be a recess formed in the driversub 240 that may be configured to receive the second split ring 250, asshown in FIGS. 19-22. In one or more embodiments, the first split ring260 and the second split ring 250 disposed within the circumferentialcavity between the hammer casing 222 and the driver sub 240 may preventinadvertent back-off, unthreading, or any other type of inadvertentdisengagement between the driver sub 240 and the hammer casing 222.

As shown in FIGS. 19-22, the first split ring 260 includes outer surfacegrooves 262 configured to engage with corresponding female grooves 226of the hammer casing 222. The outer surface grooves 262 of the firstsplit ring 260 and the female grooves 226 of the hammer casing 222 mayhave a corresponding set of flats on outer surface grooves 262 andfemale grooves 226, respectively. The outer surface grooves 262 of thefirst split ring 260 may also have ramps which correspond to ramps ofthe female grooves 226 of the hammer casing 222, similar to the ramps294 of the hammer casing 222 and the ramps 284 of the first split ring260 shown in FIG. 7. Those having ordinary skill in the art willappreciate that the first split ring 260 is not limited to includingouter surface grooves 262 and, correspondingly, the hammer casing 222 isnot limited to including corresponding female grooves 226, as will bediscussed below with respect to FIGS. 23 and 24.

Further, as shown in FIGS. 19-22, the first split ring 260 includesinner surface grooves 264 formed on the opposite side (i.e., the innerside) of the first split ring 260 from the outer surface grooves 262.Furthermore, as shown in FIGS. 19-22, the second split ring 250 includesouter surface grooves 246 formed along at least a portion of a length ofthe second split ring 250. In one or more embodiments, the outer surfacegrooves 246 of the second split ring 250 may be configured to engagewith the inner surface grooves 264 of the first split ring 260. Theinner surface grooves 264 of the first split ring 260 may permit axialmovement of the second split ring 250 relative to the first split ring260 to occur in one direction, i.e., in the direction of the arrow 266.Further, the inner surface grooves 264 of the first split ring 260 mayprevent axial movement of the second split ring 250 relative to thefirst split ring 260 in the direction of the arrow 268. The orientationof the ramp on the outer surface grooves 246 of the second split ring250 with the corresponding ramps on the inner surface grooves 264 of thefirst split ring 260 may permit the diameter of the first split ring 260to enlarge as one or more ramps of the inner surface grooves 264 of thefirst split ring 260 and one or more ramps of the outer surface grooves246 of the second split ring 250 slide past each other. The contactinterface of the above-described ramps, being in a non-perpendicularorientation relative to axial movement, may permit the relative motionbetween the first split ring 260 and the second split ring 250 to, inturn, provide sufficient radial force on the first split ring 260 toexpand the diameter of the first split ring 260, thereby facilitatingthe movement of the second split ring 250 and the driver sub 240 in onedirection relative to the first split ring 260.

When the second split ring 250 and/or the driver sub 240 is moving inthe direction of arrow 268, i.e., axially downward, the flats 288, 298of the outer surface grooves 262 of the first split ring 260 and thecorresponding female grooves 226 of the hammer casing 222, respectively,are engaged such that the axial movement of the first split ring 260relative to the driver sub 240 in the direction of arrow 266 isarrested. However, when the second split ring 250 and/or the driver sub240 is moving in the direction of arrow 266, i.e., axially upward, theflats 288, 298 are engaged such that perpendicular movement relative toarrow 266 is permitted and ramps 246, 264 of the second split ring 250and the first split ring 260, respectively, may climb past each otherduring assembly/stabbing of the driver sub 240 in the hammer casing 222.

Still referring to FIGS. 19-22, the hammer bit retainer system may beassembled such that the driver sub 240 is inserted/stabbed into thehammer casing 222 with both the first split ring 260 and the secondsplit ring 250 disposed in the circumferential cavity, e.g., thecircumferential cavity 238 shown in FIGS. 3 and 4, between an innersurface of the hammer casing 222 and an outer surface of the driver sub240. In this steady state illustration, the ramp and the flat of thefirst split ring 260, e.g., the ramp 286 and the flat 282 of the splitring 260 shown in FIG. 7, constrict around and settle into matingcontact with the ramp 276 and the flat 272 of the second split ring 250,similar to the ramp and the flat of the driver sub 240 shown in FIG. 7.In this steady state position shown in FIG. 7, the flat 298 and the ramp294 on the female grooves 226 of hammer casing 222 may not be inengaging contact with corresponding/mating ramp 284 and flat 288 onouter surface grooves of the first split ring 260. In one or moreembodiments, a slight amount of clearance may exist between theseaforementioned corresponding surfaces. This steady state position is theservice position when the hammer assembly 200 is in operational use andthe anti-backoff feature of the hammer bit retainer system is notengaged.

As discussed above, when the assembly 200 is in operation, severevibration and/or improper operational practices may create anundesirable condition in which the driver sub 240 begins to move in thedirection of arrow 268, as shown in FIG. 19. This motion, in thedirection of arrow 268, may be created when driver sub 240 begins torotate and unthread itself from the hammer casing 222 at correspondingengaged threads (e.g., engaged threads 228, 248 shown in FIG. 3). Ifleft unabated, the driver sub 240 may become separated from the hammercasing 222. However, when the hammer bit retainer system of the presentdisclosure is employed, the unabated movement of the driver sub 240 inthe direction of arrow 268 may be prevented. As discussed above, in oneor more embodiments, the hammer bit retainer system may include amulti-piece ring including the first split ring 260 and the second splitring 250.

Further, as discussed above, if the driver sub 240 begins to loosen fromthe hammer casing 222, the driver sub 240 moves axially in the directionof arrow 268 relative to the hammer casing 222. However, in thismovement direction 268, the first split ring 260 is mechanically lockedby the contact of the flats of the external circumferential grooves 246of the second split ring 250 and the flats of the inner surface grooves264 of the first split ring 260, such that both the second split ring250 and the first split ring 260 move together as a single unit.

In one or more embodiments, each of the first split ring 260, the secondsplit ring 250 and the driver sub 240 may move together as a single unitbecause the second split ring 250 may be disposed in a recess in thedriver sub 240. Further, each of the first split ring 260, the secondsplit ring 250 and the driver sub 240 may also move as a single unitbecause the grooves 246, 264 may prevent movement of the first splitring 260 with respect to the second split ring 250.

In one or more embodiments, if additional force is applied to the driversub 240 and, in turn, the second split ring 250, in the direction ofarrow 268, the ramps of the outer surface grooves 262 of the first splitring 260 and the ramps of the female grooves 226 of the hammer casing222 engage further and may force the first split ring 260 to apply ahoop stress around the second split ring 250 and the driver sub 240.This may cause the mating contacting force of the flats of the innersurface grooves 264 of the first split ring 260 and the outer surfacegrooves 246 of the second split ring 250 to be increased. Due to thehoop stress created by the ramps of the outer surface grooves 262 of thefirst split ring 260 and the ramps of the female grooves 226 of thehammer casing 222 acting on the flats of the inner surface grooves 264of the first split ring 260 and the outer surface grooves 246 of thesecond split ring 250, a mechanical lock may be generated between thedriver sub 240, the second split ring 250, the first split ring 260, andthe hammer casing 222, thereby halting any further axial movement of thedriver sub 240 in the direction of arrow 268 relative to the hammercasing 222.

As discussed above with regard to FIG. 10, to remove the driver sub 240from the hammer casing 222 (e.g., to service the hammer assembly 200), aspreading tool may be inserted into an access window, e.g., the accesswindow 224 shown in FIG. 2, to expand the split ring 260 such that theflats 272, 282 are separated with a sufficient clearance to permit thedriver sub 240 to move in the direction of arrow 268 without contactingthe split ring 260.

In another embodiment, to remove the driver sub 240 from the hammercasing 222, torque may be applied to the driver sub 240, e.g., in acounter-clockwise direction, which may force the inner surface grooves264 of the first split ring 260 to engage with the outer surface grooves264 of the second split ring 250 and may force the first split ring 260to tighten around the driver sub 240. Torque may be continually appliedto the driver sub 240 until the inner surface grooves 264 of the firstsplit ring 260 and the outer surface grooves 264 of the second splitring 250 fail in shear, which may allow the driver sub 240 to beextracted. Removing the driver sub 240 from the hammer casing 222 bytorquing the driver sub 240 until the inner surface grooves 264 of thefirst split ring 260 and the outer surface grooves 264 of the secondsplit ring 250 fail in shear may render a spreading tool and an accesswindow superfluous. As such, those having ordinary skill in the art willappreciate that the hammer assembly 200, as described herein, is notlimited to having an access window formed thereon (e.g., the accesswindow 224 shown in FIG. 2). The lack of an access window formed on thehammer assembly 200 may allow the use of the multi-piece ring (i.e., thefirst split ring 260 and the second split ring 250) to be used as ananti-backoff mechanism between the driver sub 240 and the hammer casing222 on a tool using mud circulation without concern of mud or otherfluid leaking through the access window. Thus, fluid pressure inside thecasing may also be maintained.

In one or more embodiments, the force used to shear the inner surfacegrooves 264 of the first split ring 260 and the outer surface grooves264 of the second split ring 250 can be calculated/predetermined and maydepend on the axial length of the grooves. The shear force may berelated to the torque applied and/or the thread pitch on the femalethreads 226 of the hammer casing 222 and the outer surface grooves 246of the second split ring 250. By varying the length of the inner surfacegrooves 264 of the first split ring 260 and the outer surface grooves264 of the second split ring 250, the shear force and resulting torquecan be predicted and designed to a specific value.

FIGS. 19-22 show the inner surface grooves 264 of the first split ring260 covering about 100%, 75%, 50%, and 25%, respectively, of an axiallength of the first split ring 260 (and/or an axial length of the outersurface grooves 262 of the first split ring 260). Similarly, FIGS. 19-22show the outer surface grooves 246 of the second split ring 250 coveringabout 100%, 75%, 50%, and 25%, respectively, of an axial length of thesecond split ring 250.

As shown in FIG. 19, the length of the first split ring 260 covered bythe outer surface grooves 262 is greater than about 90% (e.g., about100%) of the length of the first split ring 260. Further, the length ofthe first split ring 260 covered by the inner surface grooves 264 isgreater than about 90% (e.g., about 100%) of the length of the firstsplit ring 260. As such, the length of the first split ring 260 coveredby the inner surface grooves 264 is greater than about 90% (e.g., about100%) of the length of the first split ring 260 covered by the outersurface grooves 262. In addition, the length of the second split ring250 covered by the outer surface grooves 246 is greater than about 90%(e.g., about 100%) of the length of the second split ring 250.

As shown in FIG. 20, the length of the first split ring 260 covered bythe outer surface grooves 262 is greater than about 90% (e.g., about100%) of the length of the first split ring 260. Further, the length ofthe first split ring 260 covered by the inner surface grooves 264 isfrom about 60% to about 90% (e.g., about 75%) of the length of the firstsplit ring 260. As such, the length of the first split ring 260 coveredby the inner surface grooves 264 is from about 60% to about 90% (e.g.,about 75%) of the length of the first split ring 260 covered by theouter surface grooves 262. In addition, the length of the second splitring 250 covered by the outer surface grooves 246 is from about 60% toabout 90% (e.g., about 75%) of the length of the second split ring 250.The force used to shear the grooves 264 of the first split ring 260and/or the grooves 246 of the second split ring 250, as shown in FIG.20, may be less than the force used to shear the grooves 264 and/or thegrooves 246, as shown in FIG. 19.

As shown in FIG. 21, the length of the first split ring 260 covered bythe outer surface grooves 262 is greater than about 90% (e.g., about100%) of the length of the first split ring 260. Further, the length ofthe first split ring 260 covered by the inner surface grooves 264 isfrom about 35% to about 65% (e.g., about 50%) of the length of the firstsplit ring 260. As such, the length of the first split ring 260 coveredby the inner surface grooves 264 is from about 35% to about 65% (e.g.,about 50%) of the length of the first split ring 260 covered by theouter surface grooves 262. In addition, the length of the second splitring 250 covered by the outer surface grooves 246 is from about 35% toabout 65% (e.g., about 50%) of the length of the second split ring 250.The force used to shear the grooves 264 of the first split ring 260and/or the grooves 246 of the second split ring 250, as shown in FIG.21, may be less than the force used to shear the grooves 264 and/or thegrooves 246, as shown in FIGS. 19 and 20.

As shown in FIG. 22, the length of the first split ring 260 covered bythe outer surface grooves 262 is greater than about 90% (e.g., about100%) of the length of the first split ring 260. Further, the length ofthe first split ring 260 covered by the inner surface grooves 264 isfrom about 10% to about 40% (e.g., about 25%) of the length of the firstsplit ring 260. As such, the length of the first split ring 260 coveredby the inner surface grooves 264 is from about 10% to about 40% (e.g.,about 25%) of the length of the first split ring 260 covered by theouter surface grooves 262. In addition, the length of the second splitring 250 covered by the outer surface grooves 246 is from about 10% toabout 40% (e.g., about 25%) of the length of the second split ring 250.The force used to shear the grooves 264 of the first split ring 260and/or the grooves 246 of the second split ring 250, as shown in FIG.22, may be less than the force used to shear the grooves 264 and/or thegrooves 246, as shown in FIGS. 19-21.

As may be appreciated, the axial length of the first split ring 260covered by the inner surface grooves 264 may be between about 1% andabout 25%, between about 25% and about 50%, between about 50% and about75%, or between about 75% and about 100% of the axial length of thefirst split ring 260. As such, the length of the first split ring 260covered by the inner surface grooves 264 may be between about 1% andabout 25%, between about 25% and about 50%, between about 50% and about75%, or between about 75% and about 100% of the length of the firstsplit ring 260 covered by the outer surface grooves 262. In at least oneembodiment, the axial length of the second split ring 250 covered by theouter surface grooves 246 may be between about 1% and about 25%, betweenabout 25% and about 50%, between about 50% and about 75%, or betweenabout 75% and about 100% of the axial length of the second split ring250. In at least one embodiment, the axial length of the second splitring 250 covered by the outer surface grooves 246 may be between about1% and about 25%, between about 25% and about 50%, between about 50% andabout 75%, or between about 75% and about 100% of the length of thefirst split ring 260 covered by the outer surface grooves 262.

Those having ordinary skill will appreciate that embodiments disclosedherein are not limited to the outer surface grooves 262 of the firstsplit ring 260 forming the entire length of the first split ring 260.For example, although not shown, in one or more embodiments, the outersurface grooves 262 of the first split ring 260 may extend about 50% ofthe length of the first split ring 260. Further, in one or moreembodiments, the length of the first split ring 260 covered by the innersurface grooves 264 may be about 25% of the entire length of the firstsplit ring 260. Although, in this embodiment, the length of the firstsplit ring 260 covered by the inner surface grooves 264 may be about 25%of the entire length of the first split ring 260, it may be appreciatedthat the length of the first split ring 260 covered by the inner surfacegrooves 264 is about 50% of the length of the first split ring 260covered by the outer surface grooves 262 because the length of the firstsplit ring 260 covered by the outer surface grooves 262 is about 50% ofthe length of the first split ring 260.

Those having ordinary skill in the art will appreciate that, accordingto embodiments disclosed herein, the ratio of the length of the firstsplit ring 260 covered by the inner surface grooves 264 to the length ofthe first split ring 260 covered by the outer surface grooves 262 mayvary. For example, according to one or more embodiments, a ratio of thelength of the first split ring 260 covered by the inner surface grooves264 to the length of the first split ring 260 covered by the outersurface grooves 262 may be between about 0.01:1 and about 0.25:1,between about 0.25:1 and about 0.5:1, between about 0.5:1 and about0.75:1, or between about 0.75:1 and about 1:1.

By controlling the length of the first split ring 260 covered by theinner surface grooves 264 relative to the length of the first split ring260 covered by the outer surface grooves 262, the shear force used toshear the grooves 264, 246 of the first split ring 260 and the secondsplit ring 250, respectively, may be predicted and designed to aspecific value because the thread pitch on the hammer casing 222 and thesecond split ring 250 may be related to the torque applied. In otherwords, if a designer desires a break-out torque that is 150% greaterthan the makeup torque, the designer may calculate the axial length ofthe engaged grooves 264, 246 of the first split ring 260 and the secondsplit ring 250, respectively, to supply the desired torque. As such,both the first split ring 260 and the second split ring 250 may beexpendable components that may be replaced after each disassembly of thedriver sub 240 from the hammer casing 222.

Further, in one or more embodiments, the force used to shear the grooves264, 246 may be predicted and designed by varying the pitch and theheight of each of the grooves 264, 246 of the first split ring 260 andthe second split ring 250, respectively, as opposed to varying thelength of the first split ring 260 covered by the inner surface grooves264 relative to the length of the first split ring 260 covered by theouter surface grooves 262.

As shown in FIG. 23, in other embodiments, the hammer bit assembly 200includes a hammer bit retainer system including the first split ring 260and may not be limited to being a multi-piece ring (e.g., may not belimited to including the second split ring 250). As shown, the firstsplit ring 260 has inner surface grooves 264 formed thereon, and thedriver sub 240 has outer surface grooves 246 formed thereon. The outersurface grooves 246 of the driver sub 240 are configured to engage theinner surface grooves 264 of the first split ring 260. Further, asshown, the first split ring 260 is not limited to having outer surfacegrooves formed thereon (e.g., the outer surface grooves 262 discussedabove in FIGS. 19-22), and the hammer casing 222 is not limited tohaving corresponding female grooves (e.g., the female grooves 226 shownin FIGS. 19-22).

Furthermore, as shown in FIG. 23, the inner surface grooves 264 of thefirst split ring 260 are formed along an entire length of the firstsplit ring 260. As such, although the first split ring 260 shown in FIG.23 does not include outer surface grooves, the length of the first splitring 260 covered by the inner surface grooves 264 may be varied, such asto cover 100% of the length of the first split ring 260.

Referring to FIG. 24, the hammer bit assembly 200 includes anillustrative hammer bit retainer system having the first split ring 260and the second split ring 250, according to embodiments disclosedherein. As shown, the first split ring 260 has inner surface grooves 264formed thereon, and the second split ring 250 has outer surface grooves246 formed thereon, in which the outer surface grooves 246 of the secondsplit ring 250 are configured to engage the inner surface grooves 264 ofthe first split ring 260. Further, as shown, the first split ring 260 isnot limited to having outer surface grooves formed thereon (e.g., theouter surface grooves 262 discussed above in FIGS. 19-22), and thehammer casing 222 is not limited to having corresponding female grooves(e.g., the female grooves 226 shown in FIGS. 19-22).

Further, as shown in FIG. 24, the inner surface grooves 264 of the firstsplit ring 260 are formed along an entire length of the first split ring260. As such, although the first split ring 260 shown in FIG. 23 doesnot include outer surface grooves, the length of the first split ring260 covered by the inner surface grooves 264 may be varied, such as tocover 100% of the length of the first split ring 260.

Although the first split ring 260 shown in FIGS. 23 and 24 does notinclude outer surface grooves formed thereon (e.g., the outer surfacegrooves 262 discussed above in FIGS. 19-22), and the hammer casing 222does not include corresponding female grooves (e.g., the female grooves226 shown in FIGS. 19-22), the torque used to shear the grooves 246, 264may still be predicted and designed, as described above, by consideringthe axial length of the grooves 246, 264, as well as the pitch andlength of the grooves 246, 264. In one or more embodiments, the materialused to form the first split ring 260 and/or the second split ring 250may be considered in determining the shear force desired for the hammerbit retainer system.

In one or more embodiments, the first split ring 260 and/or the secondsplit ring 250 may be manufactured from alloy steel. For example, steelmay be alloyed with a variety of elements in total amounts of between1.0% and 50% by weight to improve the mechanical properties (e.g.,strength, toughness, hardness, wear resistance, hardenability) of thefirst split ring 260 and/or the second split ring 250. In one or moreembodiments, the first split ring 260 and/or the second split ring 250may be heat treated. Common alloys that may be used include, but are notlimited to, manganese, nickel, chromium, molybdenum, vanadium, siliconand boron. Other alloys that may be used include, but are not limitedto, aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tinand zirconium. In another embodiment, the split ring 260 may bemanufactured from a non-alloy steel. In still other embodiments, thesplit ring 260 may be manufactured from other metallic materials. In oneor more embodiments, the first split ring 260 and/or the second splitring 250 may be manufactured from non-metallic materials.

Methods of hammer bit assembly/disassembly that include the hammer bitretention system in accordance with one or more embodiments of thepresent disclosure are generally disclosed with reference to theembodiment shown in FIGS. 2-6; however, it should be understood that themethod of hammer bit assembly/disassembly disclosed herein may alsoapply to other embodiments disclosed herein. The method includesinstalling or inserting the split ring 260 in the circumferential cavity238 of the hammer casing 222. The split ring 260 may becircumferentially compressed slightly to reduce the circumference of thesplit ring 260 for insertion through the lower end portion 236 of thehammer casing 222 and into the circumferential cavity 238.

The split ring 260 is then expanded radially outward inside thecircumferential cavity 238 as the driver sub 240 is stabbed into the endof the hammer casing 222. Such expansion permits a sufficient clearancebetween an outer diameter of the driver sub 240 and an inner diameter ofthe split ring 260. The external threads 248 of the driver sub 240 arethreadably engaged with the internal threads 228 of the hammer casing222 and tightened to a specified torque, as will be known to one ofordinary skill in the art. The split ring 260 is then collapsed to anon-expanded diameter such that the split ring 260 engages the outersurface 258 of the driver sub 240.

The split ring 260 may be radially expanded in a number of ways inaccordance with one or more embodiments of the present disclosure. Incertain embodiments, as previously disclosed, the driver sub 240 may beconfigured having a tapered outer profile. As the driver sub 240 isinserted into the hammer casing 222 and through the split ring 260installed in the circumferential cavity 238, the tapered profile of thedriver sub 240 radially expands the split ring 260 by forcing the splitring 260 to climb on the tapered profile as the driver sub 240penetrates the hammer casing 222. The split ring 260 may continue toclimb the tapered profile of the driver sub 240 until the split ring 260is axially located at the proper location on the driver sub (i.e., belowor past the external threaded portion 248).

In one or more other embodiments, commercially available tools (e.g.,needle-tip pliers) may be used to manually radially expand the splitring 260 by applying opposing forces on the end portions of the splitring 260 as the driver sub 240 is stabbed into the hammer casing 222.For example, the end portions of the split ring 260 may be accessedthrough the access window 224 (FIG. 4) disposed in the hammer casing222. The pliers may be used to engage the end portions of the split ring260 (having a gap or split 270 therebetween), or in other embodiments,extensions 361 of the split ring 360 (FIG. 15), to radially expand thesplit ring 260 such that the diameter/circumference of the split ring260 is sufficiently large to allow the driver sub 240 to passtherethrough.

Once installed, the split ring 260 may remain stationary (i.e., thesplit ring 260 is substantially prevented from rotating) when thedownhole tool is in operation so that the end portions of the split ring260 remain aligned with the access window 224, thus allowing fordisassembly. To prevent the split ring 260 from rotating, a lug 290 maybe disposed in the split 270 of the split ring 260 as a stopper toprevent rotation of the split ring 260. The lug 290 may be installedafter the split ring 260 is installed in the hammer casing 222. The lug290 is disposed in the split 270 such that the middle section 292 of thelug 290 is aligned with the access window 224 of the hammer casing 222.The lug 290 may also be press fitted in the access window 224. In one ormore embodiments, the access window 224, after the lug 290 is installed,may be sealed using a silica gel or sealing material to preventparticles from entering the central bore 230 of the hammer casing 222through the access window 224. The sealing material may be removed fromthe access window 224 prior to disassembly of the driver sub 240 fromthe hammer casing 222.

To disassemble the driver sub 240 from the hammer casing 222, the splitring 260 is again expanded to disengage the inner surface grooves 264 ofthe split ring 260 from the external circumferential grooves 246 on theouter surface 258 of driver sub 240. The split ring 260 may be radiallyexpanded by engaging end portions of split ring 260 (or extensions 361of the split ring 360). The split ring 260 may be expanded via theaccess window 224 from the outside of the hammer casing 222 by expandingthe split ring 260 using pliers or other tools. Once the split ring 260is radially expanded inside the circumferential cavity 238 of the hammercasing 222, the driver sub 240 may be freely rotated and unthreaded fromthe hammer casing 222, and subsequently removed from the hammer casing222.

While embodiments described herein relate to a hammer bit lockingmechanism used to prevent a driver sub from backing off a hammer casing,it will be appreciated that the locking mechanism disclosed in one ormore embodiments herein may have utility in any number of other toolassemblies and applications which prevent or mitigate a first componentfrom axially separating from a second component.

One or more embodiments of the present disclosure provide a lockingmechanism for threaded connections of downhole percussion hammer bitsthat may be used in any conventional or state-of-the-art downhole tool.Particularly, embodiments disclosed herein prevent threaded members frombacking off (e.g., while the tool is downhole) through the use of alocking mechanism disposed between the threaded members. Thus, thelocking mechanism may have broad application and result in cost savingsas well as reduced drilling time.

For example, a split ring is assembled at the threaded connectionbetween the hammer casing and driver sub for preventing back-off due tovibrations. Locking the threaded connection with the split ring provideshigh thrust load capacity, which may translate into cost savings andimproved mechanical properties of the threaded connection andcomponents. The split ring further allows for movement in one direction,while preventing the downhole components from separating if the threadedconnection becomes loose. The split ring may be applied and removedmultiple times without damaging any parts. Finally, the split ring maybe adaptable to most downhole tools using threaded component endportions.

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from “Hammer Bit Locking Mechanism.” Accordingly, all suchmodifications are intended to be included within the scope of thisdisclosure. In the claims, means-plus-function clauses are intended tocover the structures described herein as performing the recited functionand not only structural equivalents, but also equivalent structures.Thus, although a nail and a screw may not be structural equivalents inthat a nail employs a cylindrical surface to secure wooden partstogether, whereas a screw employs a helical surface, in the environmentof fastening wooden parts, a nail and a screw may be equivalentstructures. It is the express intention of the applicant not to invoke35 U.S.C. §112, paragraph 6 for any limitations of any of the claimsherein, except for those in which the claim expressly uses the words‘means for’ together with an associated function.

What is claimed is:
 1. A hammer bit locking mechanism, comprising: adriver sub adapted to receive and movably couple to a shank of a bit,the driver sub including a portion thereof having an outer surface withone or more grooves therein; a hammer casing having a central bore andreceiving the portion of the driver sub in the central bore; and alocking device disposed between the hammer casing and the portion of thedriver sub, the locking device including an inner surface with one ormore grooves therein configured to engage the one or more grooves in theouter surface of the portion of the driver sub, the locking devicearranged and designed to prevent axial movement of the driver subrelative to the hammer casing in at least one direction.
 2. The hammerbit locking mechanism of claim 1, wherein the locking device is disposedin a circumferential cavity defining the central bore of the hammercasing.
 3. The hammer bit locking mechanism of claim 2, wherein thelocking device includes an outer surface thereof with one or moregrooves therein configured to engage one or more corresponding grooveson an inner surface of the hammer casing.
 4. The hammer bit lockingmechanism of claim 1, wherein engagement between the one or more groovesof the inner surface of the locking device and the one or more groovesof the outer surface of the driver sub prevent the driver sub frommoving axially in one direction.
 5. The hammer bit locking mechanism ofclaim 1, wherein the hammer casing has an access window arranged anddesigned to permit access to the locking device.
 6. The hammer bitlocking mechanism of claim 5, further comprising a lug disposed in theaccess window and positioned between end portions of the locking device.7. The hammer bit locking mechanism of claim 1, wherein the driver subhas a tapered outer profile along an axial length thereof, and whereinthe tapered outer profile has an angle of between 5 degrees and 30degrees relative to a central axis of the driver sub.
 8. A method ofpreventing decoupling of coupled components of a percussion hammer bit,the method comprising: inserting a locking device in a circumferentialcavity positioned in a hammer casing; expanding the locking device;inserting at least a portion of a driver sub into a central bore of thehammer casing and through the expanded locking device; and coupling thedriver sub and the hammer casing such that one or more inner surfacegrooves of the locking device engage one or more outer surface groovesof the driver sub, thereby preventing axial movement between the driversub and the hammer casing in at least one direction.
 9. The method ofclaim 8, wherein the locking device has one or more outer surfacegrooves configured to engage one or more corresponding inner surfacegrooves on the hammer casing.
 10. The method of claim 8, furthercomprising accessing the locking device through an access window in thehammer casing.
 11. The method of claim 10, further comprising installinga lug in the access window of the hammer casing, the lug arranged anddesigned to prevent the locking device from rotating.
 12. The method ofclaim 8, wherein expanding the locking device is facilitated by atapered outer surface of the portion of the driver sub being insertedinto the central bore of hammer casing and through the expanded lockingdevice.
 13. A locking mechanism of a downhole tool, comprising: a firstbody adapted to receive and movably couple to a shank of a bit; a secondbody having a central bore and receiving a portion of the first body inthe central bore; and a first split ring disposed between the secondbody and the portion of the first body, the first split ring includingan inner surface with one or more grooves formed therein and an outersurface with one or more grooves formed thereon, the first split ringarranged and designed to prevent axial movement of the first bodyrelative to the second body in at least one direction; and a secondsplit ring disposed radially within the first split ring, the secondsplit ring including an outer surface with one or more grooves formedthereon, the one or more grooves of the second split ring configured toengage the one or more grooves in the inner surface of the first splitring.
 14. The locking mechanism of claim 13, wherein an axial length ofthe first split ring covered by the grooves formed on the inner surfacethereof is between about 75% and about 100% of the axial length of thefirst split ring, or wherein an axial length of the second split ringcovered by the grooves formed on the outer surface thereof is betweenabout 75% and about 100% of the axial length of the second split ring.15. The locking mechanism of claim 13, wherein an axial length of thefirst split ring covered by the grooves formed on the inner surfacethereof is between about 50% and about 75% of the axial length of thefirst split ring, or wherein an axial length of the second split ringcovered by the grooves formed on the outer surface thereof is betweenabout 50% and about 75% of the axial length of the second split ring.16. The locking mechanism of claim 13, wherein an axial length of thefirst split ring covered by the grooves formed on the inner surfacethereof is between about 25% and about 50% of the axial length of thefirst split ring, or wherein an axial length of the second split ringcovered by the grooves formed on the outer surface thereof is betweenabout 25% and about 50% of the axial length of the second split ring.17. The locking mechanism of claim 13, wherein an axial length of thefirst split ring covered by the grooves formed on the inner surfacethereof is between about 1% and about 25% of the axial length of thefirst split ring, or wherein an axial length of the second split ringcovered by the grooves formed on the outer surface thereof is betweenabout 1% and about 25% of the axial length of the second split ring. 18.The locking mechanism of claim 13, wherein the downhole tool comprises ahammer bit.
 19. The locking mechanism of claim 13, wherein the firstbody comprises a driver sub.
 20. The locking mechanism of claim 13,wherein the second body comprises a hammer casing.